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LISTVIEW动态加载网络数据2

2011-10-14 15:12 435 查看

写的有点乱，但是写的挺好的。

转自：/article/6980298.html

总体框架：

1.滚动加载

listView.setOnScrollListener(newOnScrollListener() {

//添加滚动条滚到最底部，加载余下的元素

@Override

publicvoidonScrollStateChanged(AbsListView
view,intscrollState) {

if(scrollState==OnScrollListener.SCROLL_STATE_IDLE) {

loadRemnantListItem();

}

}

@Override

publicvoidonScroll(AbsListView
view,intfirstVisibleItem,intvisibleItemCount,inttotalItemCount) {}

});

listView.setOnItemSelectedListener(newOnItemSelectedListener() {

//按键选择List中的item，焦点落在最下面的view上加载余下的item

@Override

publicvoidonItemSelected(AdapterView<?>parent,
Viewview,intposition,longid) {

if(footerView==view) {

loadRemnantListItem();

listView.setSelection(position-1);

}

}

@Override

publicvoidonNothingSelected(AdapterView<?>parent) {}

});

privatevoidloadRemnantListItem() {//滚到加载余下的数据

//动态的改变listAdapter.getCount()的返回值

//使用Handler调用listAdapter.notifyDataSetChanged();更新数据

}

2.滚动翻页

//listView监听器代码相同

privatevoidloadRemnantListItem() {//滚到加载余下的数据

//重新listView.setAdapter(newsAdapter);

//使用Handler调用listAdapter.notifyDataSetChanged();更新数据

}

注：在listView最下面可以使用listView.addFooterView(footerView,null,true);来显示“加载中...”等的字样来美化用户体验，在loadRemnantListItem()方法中动态控制“加载中...”的显示和不显示。

具体例子1:

ListView异步加载图片是非常实用的方法，凡是是要通过网络获取图片资源一般使用这种方法比较好，用户体验好，不用让用户等待下去，下面就说实现方法，先贴上主方法的代码：

packagecn.wangmeng.test;

importJava.io.IOException;

importjava.io.InputStream;

importjava.lang.ref.SoftReference;

importjava.NET.MalformedURLException;

importjava.net.URL;

importjava.util.HashMap;

importAndroid.graphics.drawable.Drawable;

importandroid.os.Handler;

importandroid.os.Message;

publicclassAsyncImageLoader{

privateHashMap<String,SoftReference<Drawable>>imageCache;

publicAsyncImageLoader(){

imageCache=newHashMap<String,SoftReference<Drawable>>();

}

publicDrawableloadDrawable(finalStringimageUrl,finalImageCallbackimageCallback){

if(imageCache.containsKey(imageUrl)){

SoftReference<Drawable>softReference=imageCache.get(imageUrl);

Drawabledrawable=softReference.get();

if(drawable!=null){

returndrawable;

}

}

finalHandlerhandler=newHandler(){

publicvoidhandleMessage(Messagemessage){

imageCallback.imageLoaded((Drawable)message.obj,imageUrl);

}

};

newThread(){

@Override

publicvoidrun(){

Drawabledrawable=loadImageFromUrl(imageUrl);

imageCache.put(imageUrl,newSoftReference<Drawable>(drawable));

Messagemessage=handler.obtainMessage(0,drawable);

handler.sendMessage(message);

}

}.start();

returnnull;

}

publicstaticDrawableloadImageFromUrl(Stringurl){

URLm;

InputStreami=null;

try{

m=newURL(url);

i=(InputStream)m.getContent();

}catch(MalformedURLExceptione1){

e1.printStackTrace();

}catch(IOExceptione){

e.printStackTrace();

}

Drawabled=Drawable.createFromStream(i,"src");

returnd;

}

publicinterfaceImageCallback{

publicvoidimageLoaded(DrawableimageDrawable,StringimageUrl);

}

}

以上代码是实现异步获取图片的主方法，SoftReference是软引用，是为了更好的为了系统回收变量，重复的URL直接返回已有的资源，实现回调函数，让数据成功后，更新到UI线程。

ViewCache是辅助获取adapter的子元素布局

packagecn.wangmeng.test;

importjava.util.List;

importcn.wangmeng.test.AsyncImageLoader.ImageCallback;

importandroid.app.Activity;

importandroid.graphics.drawable.Drawable;

importandroid.view.LayoutInflater;

importandroid.view.View;

importandroid.view.ViewGroup;

importandroid.widget.ArrayAdapter;

importandroid.widget.ImageView;

importandroid.widget.ListView;

importandroid.widget.TextView;

publicclassImageAndTextListAdapterextendsArrayAdapter<ImageAndText>{

privateListViewlistView;

privateAsyncImageLoaderasyncImageLoader;

publicImageAndTextListAdapter(Activityactivity,List<ImageAndText>imageAndTexts,ListViewlistView){

super(activity,0,imageAndTexts);

this.listView=listView;

asyncImageLoader=newAsyncImageLoader();

}

publicViewgetView(intposition,ViewconvertView,ViewGroupparent){

Activityactivity=(Activity)getContext();

//InflatetheviewsfromXML

ViewrowView=convertView;

ViewCacheviewCache;

if(rowView==null){

LayoutInflaterinflater=activity.getLayoutInflater();

rowView=inflater.inflate(R.layout.image_and_text_row,null);

viewCache=newViewCache(rowView);

rowView.setTag(viewCache);

}else{

viewCache=(ViewCache)rowView.getTag();

}

ImageAndTextimageAndText=getItem(position);

//LoadtheimageandsetitontheImageView

StringimageUrl=imageAndText.getImageUrl();

ImageViewimageView=viewCache.getImageView();

imageView.setTag(imageUrl);

DrawablecachedImage=asyncImageLoader.loadDrawable(imageUrl,newImageCallback(){

publicvoidimageLoaded(DrawableimageDrawable,StringimageUrl){

ImageViewimageViewByTag=(ImageView)listView.findViewWithTag(imageUrl);

if(imageViewByTag!=null){

imageViewByTag.setImageDrawable(imageDrawable);

}

}

});

if(cachedImage==null){

imageView.setImageResource(R.drawable.default_image);

}else{

imageView.setImageDrawable(cachedImage);

}

//SetthetextontheTextView

TextViewtextView=viewCache.getTextView();

textView.setText(imageAndText.getText());

returnrowView;

}

}

ImageAndTextListAdapter是实现ListView的Adapter，里面有个技巧就是imageView.setTag(imageUrl)，setTag是存储数据的，这样是为了保证在回调函数时，listview去更新自己对应item,大家仔细阅读就知道了。

具体例子2:

01	package cn.riddles.activity;

03	import android.app.Activity;

04	import android.os.Bundle;

05	import android.widget.ListView;

07	public class MainActivity extends Activity {

08	private ListView lv;

@Override

10	public void onCreate(Bundle savedInstanceState){

11	super .onCreate(savedInstanceState);

12	setContentView(R.layout.main);

13	lv =(ListView) this .findViewById(R.id.test_lv);

14	lv.setAdapter( new SongListAdapter( this ));

01	package cn.riddles.activity;

03	import android.content.Context;

04	import android.util.Log;

05	import android.view.LayoutInflater;

06	import android.view.View;

07	import android.view.ViewGroup;

08	import android.widget.BaseAdapter;

09	import android.widget.ImageView;

10	import android.widget.TextView;

/**

12	* @authorriddlezhang歌曲条目适配器

*/

14	public class SongListAdapter extends BaseAdapter {

15	private static final String TAG= "SongListAdapter" ;

16	private Context mContext;

17	private String[] strings={ "王力宏" , "吴尊" , "何润东" , "金城武" , "吴彦祖" };

18	private String[] paths={ "http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/wang_li_hong.jpg" ,

19	"http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/wu_zun.jpg" ,

20	"http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/he_run_dong.jpg" ,

21	"http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/jin_cheng_wu.jpg" ,

22	"http://list.image.baidu.com/t/image_category/galleryimg/menstar/hk/wu_yan_zu.jpg" };

23	public SongListAdapter(Context mContext){

24	this .mContext =mContext;

27	public void setmContext(Context mContext){

28	this .mContext =mContext;

31	public int getCount() {

32	return paths.length;

35	public Object getItem( int position) {

36	return position;

39	public long getItemId( int position) {

40	return position;

43	public View getView( int position, ViewconvertView,ViewGroupparent){

44	convertView =LayoutInflater.from(mContext).inflate(R.layout.lv_adapter, null );

45	ImageView image=(ImageView)convertView.findViewById(R.id.image);

46	TextView songer=(TextView)convertView.findViewById(R.id.songer);

47	image.setTag(paths[position]);

48	songer.setText(strings[position]);

49	new CanvasImageTask().execute(image); //异步加载图片

50	Log.i(TAG, "execute:" +strings[position]);

51	return convertView;

view
sourceprint?

01	package cn.riddles.activity;

03	import java.io.InputStream;

04	import java.net.HttpURLConnection;

05	import java.net.URL;

07	import android.graphics.drawable.Drawable;

08	import android.os.AsyncTask;

09	import android.util.Log;

10	import android.view.View;

11	import android.webkit.URLUtil;

/**

15	* @authorriddlezhang

*
异步加载图片

*/

18	public class AsyncViewTask extends AsyncTask<View, Void,Drawable>{

19	private View mView;

20	protected Drawable doInBackground(View...views){

21	Drawable drawable= null ;

22	View view=views[ 0 ];

23	if (view.getTag() != null ) {

try

25	if (URLUtil.isHttpUrl(view.getTag().toString())) { //如果为网络地址。则连接url下载图片

26	URL url= new URL(view.getTag().toString());

27	HttpURLConnection conn=(HttpURLConnection)url.openConnection();

28	conn.setDoInput( true );

29	conn.connect();

30	InputStream stream=conn.getInputStream();

31	drawable =Drawable.createFromStream(stream, "src" );

32	stream.close();

33	} else { //如果为本地数据，直接解析

34	drawable =Drawable.createFromPath(view.getTag().toString());

36	} catch (Exception e){

37	Log.v( "img" , e.getMessage());

38	return null ;

41	this .mView=view;

42	return drawable;

45	protected void onPostExecute(Drawable drawable){

46	if (drawable != null ) {

47	this .mView.setBackgroundDrawable(drawable);

48	this .mView= null ;

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